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Original question:

BQ76952: Calibrating the device using bqStudio

BQ76952: Current calibration via BQStudio

AhtoM
Prodigy 40 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

I have built a high current circuit around the BQ76952EVM board, roughly as depicted here:
(I've effectively disconnected the on-board FETs and current sense paths to use external ones).


When calibrating Current gain via BQStudio Calibration tab, on the BQ76952EVM board (after board offset has been calibrated)




the program states that my current flow is in the wrong direction (?). (Increasing the current at which to calibrate doesn't pass).

"Current Calibration - Current flow is low or applied current to gauge does not match direction of current value entered.  Charge current is positive and discharge current is negative."

I am discharging the battery and I can measure the correct voltage drop on the Rsns with multimeter.
And yes, I have double checked the pin connections to SRP and SRN which are correctly wired (SRP on the battery minus side and SRN on pack minus side).

- After I have set the applied current to positive number instead, the calibration passes.
Overall current reading magnitude remains correct but is just with wrong sign, thus BQStudio shows positive current when discharging...

Is there any other parameter to set/calibrate, that I am missing here ?

  • 0
    TI__Genius 17755 points

    Hello AhtoM,

    From the error given, there is a chance there’s not enough current being detected by the device so it is failing. You may want to calibrate the current using Section 2.6 Current Calibration in the BQ769x2 Calibration and OTP Programming Guide instead to see if that works better.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 40 points

    EDIT:
    Following up on my previous reply, where it seemed I had it fixed but I noticed it works intermittenly.
    "
    At a first glance I got it working via BQStudio so far as well.
    I improved the external current path build and made sure that most of the connections to the gate driver signals were disconnected on the EVM, thus only affecting external circuits.

    Also, I noticed the external I2C connector is referenced to PACK- instead of BAT- (Once I had effectively removed PACK- from EVM, it was causing issues). So I made sure my external devices are properly referenced, so that the I2C works and now the BQStudio can understand even -1000mA current draw (or any other current draw) and I can do the calibration via the GUI.
    "

    The 'lack of current' didn't explain why negative, -1000mA didn't work, but 1000mA did.
    I tested the BQ calibration even with 10A discharge but to no success.
    I sometimes get an error message stating that the first two bytes of the device MAC was not recognized or smth similar (Over USB). Although communication seems fine.

    I noticed that my ability to do the current calibration via BQStudio was dependent on the battery I was using for testing,
    When using a 6S 32Ah LiPo, the current calibration was not possible with negative discharge current value.
    Only positive ones worked but that shows wrong direction when discharging.

    Using a smaller 2.2Ah 6S LiPo the current calibration passed with negative discharge currents with no problem.

    What we noticed is that the current count values for the 32Ah battery were positive and for 2.2Ah one negative, when discharging -1A.
    Not sure why is that the case and if that has an affect on the calibration ?

    Would this be the reason why we're experiencing unstable behaviour with the OTP guide as well ?

  • 0 in reply to AhtoM
    TI__Genius 17755 points

    Hello AhtoM,

    As stated in the EVM User Guide, the EVM uses a 1mOhm sense resistor and calibration at low current will result in some granularity from the current resolution. This may result in an apparent error at higher currents. Calibration at higher currents will help reduce this effect.

    I was also told it is recommended to use a power supply to try and calibrate it versus using a battery cell since there is a chance you are trying to tell bqStudio to calibrate the gain of -1000mA but the device is not seeing that much current from the battery.

    Can you share you schematic as well?

    What unstable behavior are you seeing with the OTP guide?

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 40 points

    The strangest thing. This morning everything via BQStudio worked, even with the seemingly problematic battery.

    Perhaps the EVM needed a restart. So currently not sure what exactly caused this.

    Thanks for the tips. Doing the actual calibration other than with the battery could be a good idea.